A test for comparing the means of two samples, or the mean of one sample (or even parameter estimates) with a specified value; also known as the "Student t-test" after the pseudonym of its inventor.

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Significance level in sample size calculation and in final analysis

Imagine that for the purpose of a study a sample size is computed with the following formula for a given power $1-\beta$, difference in means $\epsilon$, standard deviation $\sigma$ and significance ...
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9 views

T-test or repeated measure ANOVA?

I am a Phd student in neuroscience and not so knowledgeable in statistics. I have done an experiment and am not sure if i should use repeated measures ANOVA or independent T-test. The experiment is ...
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19 views

Degrees of freedom of t-test in multiple regression [duplicate]

In regression, $ t=\frac{\hat{\beta}-\beta}{se (\hat{\beta})} $ and the degrees of freedom of t-test is (n-k) because we estimate $\hat{\sigma}^2$ from RSS and the RSS has (n-k) degrees of freedom ...
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8 views

type 1 and type 2 errors for non-normal residuals in a regression

I did a regression and performed a normality tests on my residuals, which reject the Null Hypothesis that the residuals are normally distributed (the true distribution seems to be flatter with fatter ...
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1answer
27 views

Advantage/acceptability of using contrast codes to conduct pair-wise comparison vs. t-test on subset of data?

I conducted a study with three conditions (A, B, and C) and I want to test the difference between A and C. My default approach would be to run a t-test (or its equivalent) on a subset of the data ...
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23 views

t-Test residual analysis

I'm reading Experimental Design and Analysis by H.Seltman (http://www.stat.cmu.edu/~hseltman/309/Book/Book.pdf) and working on the provided HCI dataset (SPSS format, can be downloaded from page 143). ...
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12 views

Mann-Whitney output confusion

In an experiment I exposed each of 4 subject groups to a different condition to observe the impact on dependent variable. Assumptions for parametric tests were violated hence I decided to employ ...
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0answers
15 views

Dealing with seeming outliers in microarray gene expression data

I have the following microarray gene expression data for one gene let us say. BTW - have similar data for the same subjects across 17000 genes, so I am looking for a generalized solution. ...
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35 views

Is there a statistically significant difference between two methods, which test should I use & am I violating random assumption?

I collected data for every 2016 Republican primary that has available at least 3 polls, according to the polling data aggregated by RealClearPolitics.com. In a spreadsheet for each row which indicates ...
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16 views

Why can you use wald-test but not t-test in logistic regression

The books I read about logistic regression always use the wald-test or the lr-test for testing the significance of the coefficients. But they don't mention why others such as t-test cannot be applied. ...
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5answers
590 views

How can we ever know the population variance?

In hypothesis testing, a common question is what is the population variance? My question is how can we ever know the population variance? If we knew the entire distribution, we might as well know the ...
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1answer
17 views

How to evaluate level of significance of two similar correlations?

I have four datasets: A1, A2, B1, B2. Every dataset has between 100-300 items. Every item in every dataset has two values: x, y The goal: Find what datasets have similar x values. If the datasets ...
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20 views

Calculating standard deviations and testing the null hypothesis in a biological sample with n = 6

I am doing experiments on the viability of cells after treatment with different amounts of a certain substance. I have split my original cell line into 6 separate flasks at 3 days after unfreezing. ...
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1answer
17 views

How to work with repeated measures data paired t-test where sub groups seem to show opposite effect?

I have data that looks like this for repeated measures for the same subjects. Note, the flag column is something I just added to indicate whether there is an increase or decrease in pre vs. post for a ...
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11 views

how to do Grade prediction by previous score

My scenario is as follow: I got several years ago of my students score of school exam result and their public exam result. And I have a box-plot of the school exam score to public exam grade. I got ...
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18 views

Having difficulties interpreting t-Test [closed]

I am having a problem interpreting this following: t-Test: Two-Sample Assuming Equal Variances Can someone help! Thanks so much.
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1answer
17 views

one sample t test by grouping variable with more than 2 groups

I am having trouble finding any examples of one sample t test comparing the group mean to zero where the grouping is not binary, in R. For example comparing the heights by ethnicity to 5 ft (not ...
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22 views

t-test for panel dataset

I want to test whether the mean of my panel dataset (individual and time indices) is equal to some number (x) by using a t-test. Should I do this as first performing a t-test for each individual that ...
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32 views

Compare two groups to decide whether to drop one or not

I am conducting multivariate regression analysis. Say my model is (i index suppressed for simplicity): $$Y = \beta_{0} + \beta_{1}X_{1} + \beta_{2}X_{2} + e$$ I have a binary variable $Z$ which ...
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30 views

Is it possible to estimate the posterior distribution of the difference of two means using published t statistics?

I am interested in using summary statistics from published papers to obtain posterior distributions for the difference of two means. In the setting of the classic t-test, we can imagine measurements ...
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1answer
30 views

What is the appropriate test for comparing cost per conversion

If you have two test campaigns with these results, what test would you use to determine if the resulting cost per conversion is statistically different: Campaign 1: 100 clicks \$1 per click 25% ...
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20 views

how to report the comparison of two samples means, accounting for covariates

I have two groups, patients & controls, and a dependent variable "performance". I want to compare the means of the two groups, but after removing the effect of two confounding continuous ...
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1answer
34 views

Determining statistical significance of quintile means

I have a set of physician data which I have split into 5 somewhat equal quintiles (n's range from 44-53) based on the number of "HIV_patients_diagnosed_annually". I've then created a table showing ...
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7 views

One sample t-test with variance not assumed to represent the population?

Let's say you had a hypothetical study where you believe the sample standard deviation might be different from the population standard deviation. With a Welch's t-Test, you could work around this if ...
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2 views

Independent or dependent sample in content analysis

I am conducting a quantitative content analysis on specific crime news reports and want to explore difference in the quantitative amounts of coverage depending on whether the victim was male or ...
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74 views

Significant difference between time series - Can I do this?

I'd like to know whether the solution proposed below is valid/acceptable and any justification available. We have two biological conditions, and for each condition we measured 3 time series, so at ...
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24 views

Different sample sizes, skewed data and unequal variances

I am a bit confused regarding best statistical test to use for my data. Here is the details: I did a study to compare two independent groups; 31 patients and 60 healthy controls. I have around 50 ...
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42 views
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How to indicate whether the improvement of a ranking is statistically significant over another one in R?

I have two ranked lists of documents (List1, List2). After comparing each of them against the ground truth, I calculate precision at 5 (P@5) metric to measure how good are each of the ranked lists. ...
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36 views

p-value interpretation of Jonckheere Terpstra:one-sided or two-sided

I am using the Jonckheere-Terpstra test in order to validate the pooled t-test results. Basically, I like the JT test because of its non-parametric nature. Basically, I am now trying to understand ...
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16 views

Transformation and/or Winsorizing?

I want to compare two group of 24 and 28 people with t-test on type of activity (5 different's types of activity and a total), later one the same value will be use in regression logistic. If you ...
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12 views

Analysis for evolution of resistance

I am looking for help on an approach for analyzing evolution of resistance. I conducted an experiment in which I exposed pathogens to a constant drug concentration over 6 weeks. At each week, I tested ...
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17 views

With or without outlier and/or parametric vs non-paramteric

I'm comparing two group on the number or movie seen in the last mont (30 people in each group). Spss say that there 4 outlier but when I'm lookin with the z score I only find 1. If I do a t-test ...
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21 views

Winsorizing, just the outlier or all the value?

I have an outlier in my data set. I want to use the winsorizing quartile (to change the outlier to the 5th% and/or 95th%). Looking at the quartiles, sometimes I have more values than just my ...
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1answer
30 views

Outlier transformation for t-test

In a normally distributed sample with one outlier, some suggest changing the value of the outlier to be one unit above the next highest score. If you are doing a comparison test on two groups using ...
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3answers
59 views

What is the difference between doing a linear regression and exhaustive descriptive statistics?

I'm doing a report of the differences between women and men in their performance on a test with variables like: age, education, race and of course genre. I have two options: doing a linear ...
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29 views

Statistical test to compare two groups: Does my proposed process make sense?

Here is the situation. I am facing a comparison problem where I am trying to compare an insulated pipe with a non insulated pipe. I need to test if the use of insulation creates a significant ...
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24 views

Do I need to correct p.value from t.test?

I couldn't find my answer from previous similar posts, hence asking this silly question. I have two groups of samples, say A and B, with 3 replicates of each. I used t.test(paired=T) function in R ...
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21 views

Confidence intervals on weighted proportions

I am conducting a survey that will identify and quantify the extent to which businesses in a certain industry reuse, recycle and dispose of their waste. I am trying to figure out how I would be able ...
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1answer
35 views

F test or T test for a regression model

I am reviewing some lecture material and I was wondering if there was a typo in the material. I believe the material is trying to show the effect of multicollinearity on the independent variables in a ...
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10 views

Compare scores calculated for two groups who overlap?

I have three groups of ten children (A, B and C). They are each have different treatments (the treatments are to do with how they are taught about a certain biological feature). Two scores are ...
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3 views

How do you determine if a self-report subscale is influencing the overall self-report score's significant relationship?

I'm running a series of independent samples t-tests with a self-report and its subscale scores as the dependent variable. Both the overall score and one of the subscale scores show signficantly ...
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11 views

Can I extrapolate a mean difference from the t-statistic?

I have the t-statistic, df, p and cohen's d for the one-tailed independent samples t-tests on the difference between a parameter for cases and controls. I would like to obtain a mean difference and ...
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20 views

Can I obtain a mean difference from fold change data, number of participants and p values?

I have gene expression in fold change for cases vs controls. Therefore, below I have 4 times the gene expression of gene x in the cases compared with the controls. I have the number of participants ...
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22 views

What type of statistical analysis do I use now [closed]

I'am doing doing work on which type of stretching is best dynamic vs. static, I measured the distance in a sit and reach test before warm up then completed 2 measurements after the warm up, I have put ...
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1answer
47 views

Mann-Whitney U suitable for my analysis procedure?

I examine the relation of written language of investors and investment performance of investors. N=52 Dep. variable -> investment success; binary (1/0) (Acquisition/no Acquisition) (N = 28/22) ...
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13 views

Applying paired t-test to compare averages

So I did an experiment for 1 month where I investigated the change of pH of 3 different types of milk in the refrigerator and room temperature. I d now like to compare the results of each type of milk ...
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1answer
27 views

Do Cohen's d and Hedges' g apply to the Welch t-test?

How do you go about calculating effect size for the Welch t-test?
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203 views

Does Bonferroni apply to inference from parametric and non-parametric models?

I have run 6 independent-samples t-tests, and 4 Mann Whitney U tests. When applying Bonferroni correction, does it apply across all 10 tests? My hypotheses are that there will be 4 significant ...
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Statistical test to determine which system more accurately describes a trend

I have a known variable, for example a trend of heart rate, and two systems (A, & B) who sample this variable the same number of times but at different, unequal intervals. For example, system A ...